You must have a 1.1.1 or 1.1.2 jailbroken iPhone already for this to work (or jailbreak yours).

Here's the brief details, before we get our full guide up:

- Start with a 1.1.1 or 1.1.2 jailbroken phone with Installer.app installed.
- Plug in your phone via USB to your computer.
- Download, extract, and run iBrickr Special 1.1.3 jailbreak edition (non-member mirror) (ibrickr.exe in the archive).
- iBrickr will determine what firmware you are running on your phone and make sure you can run the update.
- iBrickr will then guide you through the process of obtaining and modifying the 1.1.3 firmware (make sure to read everything thoroughly).
- iBrickr will upload the new firmware image to your phone. Note that this only puts the file on your phone and does not modify it at all, yet.
- When iBrickr finishes (should take about 10 minutes), it will tell you to go to Installer and install the "1.1.3 soft upgrade" package. Do that.
- When the installer finishes (this should take another 10-15 minutes), your phone should reboot with a fresh activated 1.1.3 firmware.

Note: There is a bit of controversy surrounding this release. It seems NateTrue and the iPhone Dev Team have parted ways over this release - they believe the legality is questionable, NateTrue believes it is within rights. MMi remains neutral until more info is released. At the moment, it seems there's a rumble in the Bronx, so to speak.

Update: from NateTrue:

And zdziarski thinks there's more in the patches than there really is. It's just identifying pieces, so that the patcher software knows where to cut and paste and modify. And some kernel caches. Nothing big.